(1) Field of the Invention
The present invention relates to water entry of unmanned underwater vehicles and more specifically to suppression of cavity formation upon entry of such vehicles into the water.
(2) Description of the Prior Art
Underwater vehicles, such as torpedoes, are generally designed for speed, reliability and stealthy operation. Such vehicles are often introduced into the water by means of a high-speed air launch platform or via an in-air rocket launch system from a surface ship.
As is known in the art, upon impact with water of an object traveling at high-speed, a cavity is quickly established about the object behind its front most, portion. The cavity causes only the front most portion of the object to be in contact with the liquid. As a result, the body only experiences pressure drag during the cavity formation and added mass phases, i.e., when the body accelerates the fluid elements from rest. There is virtually no skin friction drag on the body. Since the cavity greatly reduces drag, the body can travel a considerable distance in the fluid before it slows to the point where the cavity closes on the underwater body.
The drag associated with an object is a function of how large, how heavy and how blunt the object entering the water is. An unmanned underwater vehicle (UUV), such as a torpedo or other torpedo-shaped object, will travel a considerable distance as it enters the water due to the formation of the cavity. This results in the need for high-speed water entries of such vehicles to be conducted in sufficiently deep water or at lower speeds. These restrictions reduce the allowable operational window for an air-dropped UUV.
What are needed are systems to increase the drag of an underwater vehicle without compromising vehicle stealth. In addition, there is a need to reduce the speed of the vehicle after entering the water to improve operation in shallow water environments. Further, the systems need to be integrated into current UUV hull configurations. Still further, there is a need that the systems not interfere with normal vehicle operations.